The topic of carbon dioxide in greenhouses follows to provide the reader a sense of proportion with respect to this beneficial gas in our environment.
Why do greenhouse growers install CO2 generators in their greenhouses?
Oklahoma State University Agricultural Extension: Greenhouse Carbon Dioxide Supplementation
Photosynthesis utilizes CO2 in the production of sugar which degrades during respiration and helps in plant growth. Although atmospheric and environmental conditions like light, water, nutrition, humidity, and temperature may affect the rate of CO2 utilization, the amount of CO2 in the atmosphere has a greater influence. Variation in CO2 concentration depends upon the time of day, season, the number of CO2-producing industries, composting, combustion, and the number of CO2-absorbing sources like plants and water bodies nearby. The ambient CO2 (naturally occurring level of CO2) concentration of 400 parts per million can occur in a properly vented greenhouse. However, the concentration is much lower than ambient during the day and much higher at night in sealed greenhouses. The carbon dioxide level is higher at night because of plant respiration and microbial activities. The carbon dioxide level may drop to 150 to 200 parts per million during the day in a sealed greenhouse because CO2 is utilized by plants for photosynthesis during the daytime. Exposure of plants to lower levels of CO2 even for a short period can reduce the rate of photosynthesis and plant growth. Generally, doubling the ambient CO2 level (i.e. 700 to 800 parts per million) can make a significant and visible difference in plant yield. Plants with a C3 photosynthetic pathway (geranium, petunia, pansy, aster lily, and most dicot species) have a 3-carbon compound as the first product in their photosynthetic pathway, thus are called C3 plants and are more responsive to higher CO2 concentration than plants having a C4 pathway (most of the grass species have a 4-carbon compound as the first product in their photosynthetic pathway, thus are called C4 plants). An increase in ambient CO2 to 800-1000 ppm can increase the yield of C3 plants up to 40 to 100 percent and C4 plants by 10 to 25 percent while keeping other inputs at an optimum level. Plants show a positive response up to 700 to need of 1,800 parts per million, but higher levels of CO2 may cause plant damage (Figure 1).
What is the significance of a CO2 concentration of 150 parts per million (PPM)? If this should happen to our atmosphere, WE ALL WOULD DIE. All life on earth would die. The Carbon Cycle is essential to all life on earth.
What would be the optimum CO2 concentration for our atmosphere? As you can see in Figure 1 above, 1,800 ppm creates the optimum level for maximum plant growth.
Figure 2 below plots the decline of atmospheric carbon dioxide, ever dropping toward the vegetation survival threshold. [Source: NOAA/NGDC Paleoclimatology Program]
Is there a health hazard from exposure to CO2? No.
According to the USDA, an atmospheric concentration of CO2 up to 10,000 ppm: “Typically no effects, possible drowsiness“. At 30,000 ppm there can be “Moderate respiratory stimulation, increased heart rate, and blood
pressure, ACGIH TLV-Short Term“. This information serves to assure you that a high concentration of carbon dioxide is most certainly not a threat to your health or safety.
Carbon dioxide, CO2, is not a pollutant but a natural mineral essential to all life on earth.
To learn the history of changes in the earth’s climate, read New Ice Age/Global Warming/Climate Change Historical News Resources, a chronological list of news stories, and scientific papers published from 1845 to 2022.
John White
Rockwall, Texas
John N. White 